Production of stereotypes



Patented Aug. 27, 1929. I

UNITED STATES 1,726,151 PATENT OFFICE.

EDWARD SIDNEY HOLE, OF LONDON, ENGLAND.

PRODUCTION OF STEBEOTYPES.

No Drawing. Application flied Kay 28, 1827, Serial No. 194,522, and in Great Britain July 16, 1926.

This invention relates to an improved method of producing stereotypes and printing surfaces. The present methods employed in the duplication or multiplication of existing raised printing surfaces in a material capable of standing the wear of printing, has generally necessitated the use of heavy, brittle and unwieldly metal stereotypes. These are expensive and difiicult to reproduce, often subject to distortion or shrinkage, costly to send through the post and easily liable to become damaged or broken.

Further, to obtain such duplication in material other than stereo metal has usually hitherto entailed the preliminary cost of an expensive die and the time necessary for its preparation.

The object of the present invention is to provide a method of obtaining stereotypes and other printing surfaces which will enable a cheap, extremely durable and accurate printing surface to be speedily obtained.

Broadly according to this invention stereotypes and like printing surfaces of a hard and durable nature and also the matrices for producing them are obtained by utilizing a suitable base, for instance paper, cellulose, paper pulp or other suitable substance which can be sub ected to the treatment referred to in the following description, impregnated with and treated with a composition which has the result of rendering the said base hard or fairly hard, after the base and impregnant have been placed in a press carrying either an original or a matrix, the base then being subjected to heat under pressure.

According to the present invention I do not propose to employ exclusively a metal or metal alloy as the material to form the stereotype or printing surface, but I subject to a special process an absorbent substance for instance filter paper, paper pulp in sheet or mass form, cellulose or the like impregnated with an aldehyde, a coal tar intermediate and a small proportion of an alkali salt. The aldehyde is formaldehyde, and the coal tar intermediate is preferably carbolic acid (phenol). The salt can be a salt of potassium, sodium or ammonium. A material selected from the chromium oxides, chromates and dichromates, for instance ammonium chromate or dichromate, is added subsequent to the amalgamation of the formaldehyde, phenol and alkali salt.

The following is a proper proportion by weight of substances which are involved in the first step'of the complete process: Carbolic acid (crystals) C H OH, 12 lbs.; formaldehyde (40%) UH O, 12 lbs.; potassium hydroxide KOH, 2 to 6 ozs.

These substances are intimately mixed in a suitable container, preferably enamel lined, and with constant stirring brought to boiling point. At about this stage the seething and efl'ervescence can be intensified if a piece of aluminum metal is placed in the mixture and left there throughout the process. Though practically unafl'ected the aluminium serves to emphasize the progress of the reaction. The same effect can be produced by a little boric acid, a suitable amount commensurate with the proportions of substances quoted being A; to of an ounce.

The mixture is kept boiling, preferably with constant stirring, until this first seething has subsided and until, after an interval, a second seething begins to appear. It is chiefly to indicate this stage by making the second seethin more evident, that the addition of aluminium or boric acid is useful as otherwise it is not so easy to follow the progress. At this point the strong smell of formaldehyde begins to disappear and is replaced by a not unpleasant aroma. Great care must be exercised that the boiling is not carried too far or the whole mixture may suddenly solidify into an insoluble mass. Moreover, if the mixture is boiled too much it will not have sufiicient plasticity or solubility for the purpose in view and if it is not boiled enough it will be too thin and too fluid. The more the mixture is boiled the less chromate can be used, and the adjustment of the amount of chromate to the degree of boiling gives some latitude in the operation of the process. As a rough guide it may be indicated that if on the foregoing quantity the heat applied requires 30 minutes to produce the first seething, the mixture will be ready after about another 30 minutes of the same heat. Varying quantities require varying times according to the degree of heat applied and the amount of potassium salt used. When this stage is reached and the well known pungent smell of formaldehyde has become hardly noticeable, a quantity of cold water is added which reduces the temperature and may produce a slight cloudiness in. the mixture which will disappear when the continued heat again raises it to boiling point. A suitable quantity of water is about 2 lbs.

The mixture is now cooled to about normal atmospheric temperature b any suitable cooling means, and I then ad a previously preared solution of: Ammonium dichromate (NIL),Cr O,, 2 to 5 02s.; ammonium hydroxide .880, 4 to 8 02s.; water, 4 to 8 lbs. I also find it useful to include in the above solution about A oz. of copper hydroxide. Instead of the ammonium dichromate the proportionate amount of ammonium chromate can be used. When the above solution has been added to the mixture it is well stirred and then if necessary a small quantity of methylated spirits (3 to 12 ozs.) or other form of alcohol is added, and a small further excess of ammonium hydroxide. This combination has the etiect of keeping the mixture in its water-soluble state despite the addition of the dichromate, the importance of which will appear hereafter.

A further addition of glycerine, from 2 to 6 ounces, can be made to the mixture for reasons which will also appear hereafter.

Other chromates can be used but I prefer the ammonium salt on account of the volatility of the ammonium and the comparative ease with which it effects combination. When for any purpose it is desired that the product should dry rapidl it is preferable to use calcium chromate. godium or potassium chromate or dichromate are less useful on account of the potassium already incorporated in the mixture. Chromate acid (c iromium trioxide) can also be used. but has a tendency to cause precipitation when used alone. Copper, aluminium, zinc and other metallic chromates can be used, preferably dissolved in a sufiicient quantity of chromium trioxide and water. It is also possible first to neutralize the KOH with an acid, for instance nitric or hydrochloric acid, adding a smaller quantity of ammonium dichromate afterwards.

\Vith the mixture, which has now a more or less syrupy consistency according to the degree of boiling and the amount of water used in the foregoing processes, I proceed to impregnate, for instance, sheets of filter paper, (some grades of commercial blotting paper can be also used but are not so reliable), cellulose or paper pulp, either by means of immersion, spraying, coagulation, or with a brush, and these sheets are hung to dry at ordinary atmospheric temperature upon lines. If the base is in mass or powder form it can be dried in shallow trays. The sheets or pulp can be made to dry more thoroughly for certain purposes by means of the revious addition to the mixture of a smal quantity of I some drying salt, for instance calcium borate,

or on the other hand their drying can be re-.

tarded as previously indicated by the addition of a quantity of glycerine.

For ordinary purposes-and to secure dee impressions the sheets should not be allowe to dry hard and stiff but should be used while containing suificient retained moisture orglycerine to make them soft and flexible. After some hours u )on the lines it is advisable to remove t e sheets and to store them in some air-proof container in a cool place ready for use as required.

These impregnated sheets can be used for the production of both intaglio matrices and stereos in relief. The matrix, however, is usually easier to produce as it is simply necessary to press the plates or type into the surface. \V hen duplicating from the matrix, however, it is necessary to mould the stereo sheets to project beyond their own normal surface. Therefore the sheets used for the inta lio matrices may be much dryer and less plia le than those used for making the stereos in relief. The effect of a sufficient quantity of a chromium salt is to prevent the matrix adhering to a stereo made of the same material. This effect can be enhanced if a greater quantity of chromate is introduced into the sheets intended for use as matrices. This can be done for instance, if a number of the ordinary sheets, after partial or complete drying, are immersed in a two-five per cent solution of ammonium or other chromate or dichromate preferably with an excess of ammonium hydroxide added to facilitate the absorption of the solution by the sheets. These sheets are then hung up again until dry and can then be distin uished from the ordinary sheets by a somew hat deep red colour and by their greater stiffness and lack of flexibility. The extra amount of dichromate thus introduced into the sheets used for matrices will effectivelv' prevent the sheets used for stereos from a ering to them, and will also further strengthen the matrix. A hundred or more stereos can easily be taken from a single matrix.

When it is desired to obtain reproductions of blocks, cliches or plates with only very shallow etching (for example the half-tone blocks used for newspaper photographs) it is only necessary to clean the surface of the block with plumbago or talcum-powder or a paste of these made with olive oil, Vaseline, or certain other similar vehicles.

The number of sheets of impregnated filter paper to be used depends upon the thickness of the matrix or stereo which it is desired to make. For deep line engravings about eight sheets of ordinary filter paper may be used for the matrix, and one less for the stereo, but for shallow etching three or even two sheets may serve.

It is characteristic of the mixture with which the sheets are impregnated that under the influence of sufiicient heat it is rendered temporarily fluid, while the continuance of the heat makes it then become solid, and if the process has taken place under sufiicient pressure the resultant product will have great strength and durability. This fact is taken advantage of in the manner now described.

The sheets are pressed upon the selected goo temperature being approximately. 300 degrees Fahrenheit. Still better results can be obtained if the platen which bears against the sheet of impregnated material (usually the top platen) is hotter than the other platen,

for instance about 340-360 degrees Fahrenheit. As a general rule the late or type should be heated in the press be ore the sheets are imposed thereon, as this will revent the entire or too copious flow of the impregnant from the surface to the sunken parts. Thus under the influence of simultaneous heat and pressure an exact reproduction of'the late or type will be sunk into the'imposed s leets.

The length of time of the pressing operation varies according to the degree of heat employed, the relief of the printin surface, the proportion of moisture in the s eets and the number of sheets forming the matrix. However the pressing operation need not in most cases exceed six'minu tes, and normally it need only take three minutes.

In order to prevent the back sheetsticking to the exposed platen of the press Insually cover this sheet with an extremely thin plate of steel the surface of which, next to the impregnated sheet, iswiped over with a mixture of Vaseline and talcum-powder, so that only an almost imperceptible film remains. To this plate the sheets will not adhere except, perhaps, slightly at the edges from which however they can be easily and cleanly detached.

When the sheets are removed from the press they will be in a tough consistent and some- 'what flexible board which will stand con-' siderable rough usage and cannot be easily broken. If there is any tendency of the sheets to stick to the printing plate, it is due to the exuded excess of impregnating substance hardening not under pressure around the edge of the matrix or printing plate. "By inserting a sharp tool under the edge of the matrix or late the separation becomes easy.

efore thymatrix can be used for repro- 'duction it m'ustbe thoroughly cooled. The surface of the matrix should be brushed over with a mixture of a'vehicle such as Vaseline or olive oil made into a paste with talcumpowder or plumbago or the like, which should then be well brushed out of the crevices of the matrix. This should be done each time a new stereo is to be taken from the matrix.

This matrix can now be employed for reproducing from it any desired number of copies of the original printing late by merely substituting the matrix for t e print the (press are heated by any suitable means, a v

ing plate and repeatin theoperation', with l the following modifications. The cold matrix bearing the superimposed impregnated sheets is placed, upon a cold metal late of to of any inch thick, the press ing brought into operation as speedily as possible. By this means the heat of the platen applied directly to the impregnated sheets has its effect upon those sheets considerably in advance of the heat of the other platen which must traverse both the plate upon which the matrix is placed and the matrix itself, and consequently at first the impregnating substance will tend to move towards the surface and into the recesses of the matrix where the pressing action has preceded the action of the heat, thereby obtaining a reproduction having the finest detail (provided.

the etching is not so deep as to require the special treatment hereinafter described) and hardened on the arrival of the delayed heat which has traversed the iron plate and matrix. A metallic or artially metallic surface may be secured by usting or brushing the surface of the outer impregnated sheet with the-desired metal in powder form before it is placed in contact with the matrix.

When medals, zincos and other originals are to be reproduced, and the recesses 1n the matrix are very deep, these recesses can, before the pressing operation, be fi-lled in with matter that will unite with the impregnating substance of the im osed sheets. The filling substance is prefera ly absorbent but an absorbent'filler may be mixed in certain proportions with finely powdered metallic substance for instance zinc. A suitable compound can stirred into the mixture and allowed to stand for some minutes, and is then intimately mixed with the wood flour and afterwards dried, first at a gentle heat and then at a temperature up to 300 Fahrenheit. When thoroughly dry this impregnated wood flour can be ground to a very fine and hard powder. The exact amount of chromic acid to be used depends upon the amount of potash in the original mixture and the degree to which it has been boiled. If too little chromic acid is used the resultant powder may be too light and soft for the purpose, and if too much is used the stereos may be too brittle. copper, aluminium or other metallic chro mates can be used dissolved in the chromic acid, or calcium ehromate may be used in place of or in addition to chromic acid. A very large number of metallic salts and metals in powder form can be mixed with the wood flour during impregnation and an actual printing surface largely or almost entirely,

metallic can be secured. \Vhen inserted into the sunken parts of the matrix the powder will resist the applied pressure and will also absorb the exuding impregnant so as to form a perfect replica in relief of the intaglio parts of the matrix; By means of this powder and the impregnated sheets an exact copy can be taken of a-line block the entire thickness of which has been sunk into the matrix. Not merely the surface, min the case of shallow etchings, but the whole thickness of the plate will stand out from the backing of the impregnated sheets, which even the greatest pressure (\vithout" the aid of the powder) could only force into partial conformation with the dcepl'ys unken parts of the matrix.-

The powder above described becomes an integral part of thestereo forming. with the sheets a strong whole which .can'be cut or sawn as required. \Vhen taken from the press the stereos can, moreover, vbe bent into any shape and they retain a degree of flexibility even when they have become quite cold.

' inonotype, linotypc, or other printing surfaces where there is, no airtight background but invariably a large number of crevices and lntersticesbetween the letters or lines,

it is advisable to proceed in the following manner. A paste of talcum owder or plumbago or a mixture of bot and water is spread over the surface of the type, several sheets of blotting paper placed over the "whole, which is then dried under heat and pressure in the ress. The surface of the type is then brusiied clean while the talcumpowder is left in the crevices beneath the actual printing surface where it was forced by the blotting. paper. This can be done, for instance, by means of an ordinary brush attached to the sides of which are twopieces of flat wood beyond which'the hairs of the brush barely project. By drawing this over the surface it is cleaned to' the required depth. The talcum-powder remaining in the crevices will absorb the/excess of exuding impregnant which might otherwise pass between the lines and letters and make it very difiicult for the type to .be separated. Further, insteadof using many sheets of impregnated paper as in the case of plates or other originals presenting a solid background, it is. advisable'to interleave dry sheets of filter paper between the impregnated sheets so that no more impregnant shall flow into the type and talcum-powd than is necessary to get. suflicient depth in the matrix. Perfect results from type and from type and illustration mixed can be secured by means of three or four sheets of impregnated p'aper'interleaved with three or four sheets of dry filter paper. The type should be heated before the impregnated sheets are imposed as this impedes the flow of the impregnant into the-crevices where it is not wanted. Instead of interleaving plain sheets it.is possible to dilute the impregnant (without glycerine) with 33 to 100% its weight in water, to which sufficient alcohol has been added to keep the impregnant in solution. These thinly impregnated sheets are treated with a 2 to"5% solution of a ch'romate as already described.

The stereos produced from the matrices described in this process can be made of uniform thickness with only the 'very' slightest variation, but wherey'for any purpose the thicknes's'of each stereo must be absolutely exact this can be secured by sandpapering or planing the back-in a suitable machine.

Otherwise the sole plant required to operate 4 theproces s is one heated press. The stereos can be strenghtened by utilizing for instance a sheet of textile at the back of or among the impregnated sheets.

The stereos? made by this process are resistant to any further application of heat, and an important consequence of this is that these stereos can be incorporated with the ordinary metallic type in cases where a flong matrix has to betaken of a composite page for reproduction by the ordinary casting .process. If the matrices are used for casting metallic stereos they will outlast several ordinary flong matrices and give more perfect and deeper replicas of the originals.

It will be appreciated that the present 1nvention in one embodiment briefly cons sts in obtaining printing surfaces from origiiio nals by pressing a matrix obtained from a porous fibrous or cellulose substance impregnated with formaldehyde, 0. coal tar intermediate, an alkali salt and a salt of chromium, upon a printing plate or ty e at considerable pressure, and allowing t a matrix to become cold. Y I By means of my invention printing surfaces are obtained which are more durable than most cast-metal printing surfaces and cheaper to produce, a useful feature of my invention residin in the flexible nature of the printing sur ace when firstproduced and lengthy process involved in the prepara lion of a number of similar printing su r aces.

I claim 1. The method of making printing plates and matrices therefor which consists in impregnating a sheet of plastic material with a.

, phenolic comlensation product in moist and water-soluble state and containing material selected from the chromium oxides, chromates and (licllromates, subjecting said sheet to a dr 'ing process, placing said sheet in a press carrying an original and subjecting the sheet whilst in contact with said original to heat and pressure suflicient to harden said phenolic condensation product and to convert it to the non-watcr-soluble state.

2. The method of making matrices for printing plates which consists in impregnating a sheet of plastic'n'iaterial with a phenolic condensation product in a moist and water soluble state and containing material selected from the chromium oxides, chromates and dichromates, in partially drying said sheet, in imn'iersing said sheet in a solution of ammonium dichromatc, in subjecting said sheet to a further drying operation, in placing said sheet in a press containing an original and in subjecting said sheet whilst in contact with said original to heat and pressure suflicient to harden said phenolic condcnsation.product and convert it to the nonwater-soluble state. i

3. The method of making printing plates and matrices therefor which consists in impregnating a sheet of plastic material with a phenolic condensation product in moist and water-soluble state antkcontaining a chr0- mate, subjecting said sheet to a drying proc-' ess, placing-said sheet in a press carr ing an original and subjecting the sheet w iilst in contact with said original to heat and pressure sullicient to harden said phenolic condensation product and to convert it to the non-water-soluble state.

4. The method of making matrices for printing plates which consists in impregnating a sheet of plastic material with a phenolic condensation product in a moist and water soluble state and containin chromate, in pa rtially drying said sheet, in immersing said sheet in a solution of ammonium dichromate, in subjecting said sheet to a fur her drying operation, in placin" said sheet in a press containing an originaf and in subjecting said sheet whilst in contact with said original to heat and pressure sutiicient to harden said phenolic condensation product and convert it to the non-water-soluble state.

EDWARD SIDNEY HOLE. 

